Re: [RESEND PATCH v9 04/14] iomap: Add flags parameter to iomap_page_create()

[Matthew Wilcox <willy@infradead.org>]

On Thu, Jun 23, 2022 at 10:51:47AM -0700, Stefan Roesch wrote:
> Add the kiocb flags parameter to the function iomap_page_create().
> Depending on the value of the flags parameter it enables different gfp
> flags.
> 
> No intended functional changes in this patch.

[...]

> @@ -226,7 +234,7 @@ static int iomap_read_inline_data(const struct iomap_iter *iter,
>  	if (WARN_ON_ONCE(size > iomap->length))
>  		return -EIO;
>  	if (offset > 0)
> -		iop = iomap_page_create(iter->inode, folio);
> +		iop = iomap_page_create(iter->inode, folio, iter->flags);
>  	else
>  		iop = to_iomap_page(folio);

I really don't like what this change has done to this file.  I'm
modifying this function, and I start thinking "Well, hang on, if
flags has IOMAP_NOWAIT set, then GFP_NOWAIT can fail, and iop
will be NULL, so we'll end up marking the entire folio uptodate
when really we should only be marking some blocks uptodate, so
we should really be failing the entire read if the allocation
failed, but maybe it's OK because IOMAP_NOWAIT is never set in
this path".

I don't know how we fix this.  Maybe return ERR_PTR(-ENOMEM) or
-EAGAIN if the memory allocation fails (leaving the NULL return
for "we don't need an iop").  Thoughts?